Loops in DNA: An overview of experimental and theoretical approaches

DNA loop formation plays a central role in many cellular processes. The aim of this paper is to present the state of the art and open problems regarding the experimental and theoretical approaches to DNA looping. A particular attention is devoted to the effects of the protein bridge size and of protein induced sharp DNA bending on DNA loop formation enhancement.     

Baer and Baer *-ring characterizations of Leavitt path algebras

We characterize Leavitt path algebras which are Rickart, Baer, and Baer ?-rings in terms of the properties of the underlying graph. In order to treat non-unital Leavitt path algebras as well, we generalize these annihilator-related properties to locally unital rings and provide a more general characterizations of Leavitt path algebras which are locally Rickart, locally Baer, and locally Baer ?-rings. Leavitt path algebras are also graded rings and we formulate the graded versions of these annihilator-related properties and characterize Leavitt path algebras having those properties as well.Our characterizations provide a quick way to generate a wide variety of examples of rings. For example, creating a Baer and not a Baer ?-ring, a Rickart ?-ring which is not Baer, or a Baer and not a Rickart ?-ring, is straightforward using the graph-theoretic properties from our results. In addition, our characterizations showcase more properties which distinguish behavior of Leavitt path algebras from their $C^{?}$-algebra counterparts. For example, while a graph $C^{?}$-algebra is Baer (and a Baer ?-ring) if and only if the underlying graph is finite and acyclic, a Leavitt path algebra is Baer if and only if the graph is finite and no cycle has an exit, and it is a Baer ?-ring if and only if the graph is a finite disjoint union of graphs which are finite and acyclic or loops.     

Spherical Particle in Nematic Liquid Crystal Under an External Field: The Saturn Ring Regime

We consider a nematic liquid crystal occupying the exterior region in \({\mathbb {R}}^3\) outside of a spherical particle, with radial strong anchoring. Within the context of the Landau-de Gennes theory, we study minimizers subject to an external field, modeled by an additional term which favors nematic alignment parallel to the field. When the external field is high enough, we obtain a scaling law for the energy. The energy scale corresponds to minimizers concentrating their energy in a boundary layer around the particle, with quadrupolar symmetry. This suggests the presence of a Saturn ring defect around the particle, rather than a dipolar director field typical of a point defect.     

欧式双向期权的两种定价比较

在股票价格服从泊松跳模型下,分别利用保险精算方法与无套利定价方法给出了欧式双向期权的定价公式;通过对这两种结果的比较发现,当股票价格服从特定的泊松跳模型时两种定价公式是相同的.     

Haloacetylated enol ethers: 4 [6]. Synthesis of 4-trihalomethyl-2-methylthiopyrimidines

The synthesis of a series of 5- and 6-substituted 4-trihalomethyl-2-methylthiopyrimidines, prepared from the cyclocondensation reaction of β-alkoxyvinyl tri[fluoro]chloromethyl ketones with 2-methyl-2-thiopseudourea sulfate, are reported. A systematic study to find the best reaction conditions were carried out.     

Complexing Power of Vitamin D3 Toward Various Metals. Potentiometric Studies of Vitamin D3 Complexes with Al3+, Cd2+, Gd3+, and Pb2+ Ions in Water–Ethanol Solution

This study reports the stability constants of complexes with vitamin D₃ and Al³⁺, Cd²⁺, Gd³⁺ and Pb²⁺ ions in a water–ethanol medium (30/70% v/v at 25.0°C). The logarithms of the overall stability constants are: ₁ = 12.4 ± 0.5, 7.6 ± 0.3, 9.33 ± 0.07, and 9.1 ± 0.5, respectively, whereas the logarithms of ₂ are 24.4 ± 0.5 (Al³⁺), 14.3 ± 0.3 (Cd²⁺), and 15.4 ± 0.5 (Pb²⁺). Gd³⁺ forms only the 1:1 complex. These values are compared to those reported previously and correlations are established between the stability constants and physical properties, such as the ionization energy.     

THE PREPARATION AND CHARACTERIZATION OF SBR／PS CORE-SHELL PARTICLES BY GAMMA IRRADIATION

A kind of core(SBR)-shell(PS) particles was synthesized by using SBR latex and grafting with St under gamma irradiation. The influences of absorbed dose and dose rate on the grafting yield of PS on SBR seed latex have been investigated. Results show there was a transition layer which contained the SBR/PS graft copolymer between the SBR core and PS shell. Dynamic laser scattering (DLS) and differential scanning calorimetry (DSC) results confirm the existence of grafted polystyrene, and transmission electron microscope (TEM) observation verifies the core-shell structure of SBR-g-PS latex. Such SBR/PS core-shell latex could be processed easily to ultrafine rubber powders by using spray drying and expected to be used as an impact modifier for PS.     

Fluorescence Study of DNA–Dye Complexes Using One-Photon and Two-Photon Picosecond Excitation

Preliminary results of investigation of one-photon- and two-photon-induced fluorescence of acridine orange (AO), epirubicin (ER), hypericin (HYP), and ethidium bromide (EB) in complexes with DNA are presented. A spectrofluorometer based on a picosecond Nd:YAG laser was used for investigations of two-photon (1064-nm, 1-mJ, 40-ps) and one-photon (532- and 355-nm) dye excitation. The spectra of two-photon-induced fluorescence of dyes and their complexes with DNA as well as the kinetics of dyes' fluorescence intensification during their interactions with DNA in dependence on the biomacromolecule concentration were obtained. The intensities of AO, HYP, and EB fluorescence were increased 2.4, 3.2, and 8 times, respectively, after binding with DNA at two-photon excitation, while at one-photon excitation the corresponding values were 2.5, 3.7, and 10 times. The difference in fluorescence enhancement during DNA–dye complex formation at linear and nonlinear excitation may possibly be associated with the fact that the cross sections of one-photon and two-photon absorption, in general, change unequally during the binding of dyes to organic molecules and bathocromic shift of the electronic transitions. It was shown that the peak of AO fluorescence shifted to a longer wavelength on 10 nm after two-photon excitation at 1064 nm in comparison with one-photon excitation at 532 nm.     

A new rearranged chamigrane sesquiterpene from Laurencia okamurai

A new rearranged chamigrane sesquiterpene,named laurenokamurin,was isolated from the marine red alga Laurencia okamurai.Its structure was determined on the basis of spectroscopic methods.